1. Field of the Invention
The present invention generally relates to a device for moving rollers in a printing press.
2. Background Information
Generally, a printing unit of a printing press will have disposed therein a plurality of rollers mounted for rotation within the printing unit. In order for a successful printing run to be undertaken, it is generally important that these rollers be able to move in a substantially unhindered manner.
It has often been the case that restricted movement of rollers can potentially provide detrimental effects in operating a printing unit of a printing press. Although the restrictions on the movement of a roller could possibly arise from any number of factors, it is generally recognized that greater freedom of movement, for the rollers, will provide markedly improved printing results.
Typically, the rollers of a printing unit are arranged in a chain, usually extending from the upper portion of the printing unit to the region of the plate cylinder and blanket cylinder. Various possible arrangements are feasible with regard to such chains of rollers, and in many instances, a chain of rollers can involve a relatively complicated structure. On the other hand, chains of rollers having a simpler pattern have been used.
Typically, one or more of the rollers of a printing unit will be mounted only for rotational movement. Thus, such rollers will typically extend between the sides of the frame of the printing unit in question, and will usually be mounted in a simple rotational bearing in the sides of the printing unit frame. Accordingly, such rotational bearings may, for the most part, be considered to be fixed, involving no more complicated a structure than that which is necessary to simply hold portions or extensions of a roller in place, only allowing such portions or extensions of a roller to rotate. As a result, rollers mounted in such a manner will generally be hindered from moving in a translational manner, that is, in a manner that would effectively involve movement of the rotational axis of the roller in question. Such rollers also will typically be hindered from being displaced axially, that is, in a linear direction that is parallel to the rotational axis of the roller.
On the other hand, it is known to permit a selected roller or rollers of a printing unit to be movable not only in a rotational direction but also in an axial direction. Such axial movement can also be permitted while the roller is rotating, thereby allowing the roller to undergo a simultaneous rotational and axial displacement during operation of the printing unit. Depending on the positioning of such a roller relative to other rollers in the printing unit, such a roller may be termed a "distributor roller". Distributor rollers, per se, are quite well-known and may involve any of a wide variety of arrangements for affording axial displacement of the same simultaneously with rotational displacement.
On printing forms which have different surface coverages in the individual ink zones, one problem is that the desired thickness of the ink in the zones which have only a very low ink coverage tends to be overrun by the neighboring zones which have a higher ink coverage, and the result is an undesirable equalization of the thicknesses of the ink layers. The same problem occurs if, while the printing machine is running, brief interruptions in printing are necessary, during which the paper feed and ink feed are briefly shut off and the inking unit continues to rotate. In these situations, the result is an ink profile across the width of the inking unit which is modified by the lateral spreading of the ink by rubbing, to the extent that the ink profile achieved on the printing plate hardly has anything to do with the actual ink requirement.
To correct these problems, German Patent No. 41 40 048 A1 teaches that the drive of a distributor roller can be interrupted by means of a clutch, so that the periodic axial motion of the distributor roller can be stopped. The disadvantage of this known solution is that it presents problems in terms of the re-engagement of the distributing rollers in the correct phase when printing resumes, e.g. once the interruption in the printing is over and the paper feed is resumed. If there are several distributing rollers in an inking unit, these distributing rollers normally do not tend to execute their axial stroke in synchronization, which means that they require quite a complex control system to re-establish the previously specified axial stroke. A modification of the axial stroke movement of the individual distributing rollers would likely have a direct effect on the result of the printing, and would lead to an undesirable change in the ink profile achieved.
With a known device of this type (German Patent No. 25 14 414 C3) a separate drive cylinder is used to reciprocate distributor rollers, wherein the drive cylinder axially reciprocates distributor rollers via a lever arrangement in connection with a bell-crank lever and a thrust rod. In this case, the drive cylinder is driven by a separate drive, a prerequisite being a control unit ensuring that the drive is synchronized with the machine speed. The conventional solution includes a large number of bearings which may cause clearance, or play, especially at the point of reversal of a respective distributor roller. This may be disadvantageous to the inking of the printing plate. Furthermore, this known solution requires considerable structural efforts with regard to the drive problems, thus inevitably involving high costs. In addition, connecting several distributor rollers is essentially not novel in printing-machine engineering.